My current understanding is that the reserve rate is now 0% https://www.federalreserve.gov/monetarypolicy/reservereq.htm , so it can all be loaned out.
OTOH, the Fed has other mechanisms for encouraging bank reserves -- I believe they still pay interest on any excess reserves that banks hold at the end of each day. That rate (the "IOER rate") is (still) significantly higher[1] than the federal funds rate[2], so banks can essentially collect free money by keeping any reserves at all.